Woosoon Yim

An artificial muscle actuator for biomimetic underwater propulsors

In this paper, we introduce the analytical framework of the modeling dynamic characteristics of a soft artificial muscle actuator for aquatic propulsor applications. The artificial muscle used for this underwater application is an ionic polymer-metal composite (IPMC) which can generate bending motion in aquatic environments. The inputs of the model are the voltages applied to multiple IPMCs, and the output can be either the shape of the actuators or the thrust force generated from the interaction between dynamic actuator motions and surrounding water. In order to determine the relationship between the input voltages and the bending moments, the simplified RC model is used, and the mechanical beam theory is used for the bending motion of IPMC actuators. Also, the hydrodynamic forces exerted on an actuator as it moves relative to the surrounding medium or water are added to the equations of motion to study the effect of actuator bending on the thrust force generation. The proposed method can be used for modeling the general bending type artificial muscle actuator in a single or segmented form operating in the water. The segmented design has more flexibility in controlling the shape of the actuator when compared with the single form, especially in generating undulatory waves. Considering an inherent nature of large deformations in the IPMC actuator, a large deflection beam model has been developed and integrated with the electrical RC model and hydrodynamic forces to develop the state space model of the actuator system. The model was validated against existing experimental data.

Feedback linearization and solar pressure satellite attitude control

The question of large angle pitch attitude maneuver of satellites using solar radiation pressure is considered. For pitch axis maneuver, two highly reflective control surfaces are used to generate radiation moment. Based on dynamic feedback linearization, a nonlinear control law is derived for large pitch attitude control. In the closed-loop system, the response characteristics of the pitch angle are governed by a fourth-order linear differential equation. Robustness of control system is obtained by the integral error feedback. Simulation results are presented to show that in the closed-loop system, attitude control of the satellite is accomplished in spite of the parameter uncertainty in the system.

Adaptive control of a flexible joint manipulator

In this paper the control of a flexible joint manipulator is designed using an adaptive output-feedback controller based on the backstepping design. The parameters of system are assumed to be unknown and only the motor position and link position measurements are used for the synthesis of the controller. A canonical state representation of the system is derived and filters are designed to obtain estimates of the derivatives of motor angle and link angle. Then an adaptive control law for the trajectory control of link displacement angle is derived. Compared to the same adaptive controller which only measures the link displacement angle, the order of the proposed controller is halved (order of 2) and the complexity of the control law can be reduced dramatically. Also, the proposed controller does not require the bounds on uncertain parameters for the control law derivation as compared to other output adaptive control laws.

State feedback control of an aeroelastic system with structural nonlinearity

The paper treats the question of state variable feedback control of prototypical aeroelastic wing sections with structural nonlinearity. This type of model has been traditionally used for the theoretical as well as experimental analyses of two-dimensional aeroelastic behavior. The chosen dynamic model describes the nonlinear plunge and pitch motion of a wing. A single control surface is used for the purpose of control. A control law is designed based on the state-dependent Riccati equation technique. Unlike feedback linearizing control systems reported in literature, this approach is applicable to minimum as well as nonminimum phase aeroelastic models. The closed-loop system is asymptotically stable. Simulation results are presented which show that in the closed-loop system, flutter suppression is accomplished.

Nonlinear inverse and predictive end point trajectory control of flexible macro-micro manipulators

This paper presents a new approach to end-point trajectory control of flexible macro-micro manipulator based on nonlinear inversion and predictive control techniques. In this approach, precise control of the end-effector trajectory is accomplished by the inverse controller of the rigid micro manipulator, and the predictive controller steers the end point of the flexible macro manipulator with limited elastic oscillation. The predictive control law is obtained by minimizing a quadratic function of the tip tracking error, the elastic deflection, and the input torque of the flexible macro manipulator. The feedback parameters of the predictive controller are chosen such that zero dynamics are asymptotically stable. The combination of the inverse and the predictive controllers accomplishes precise end-effector trajectory tracking and elastic mode stabilization. These results are applied to a planar macro-micro manipulator system consisting of one flexible link and two micro rigid links. Simulation results are presented to show that in the closed-loop system time varying end point trajectory control and elastic mode stabilization are accomplished.

Ionic Polymer-metal Composites for Underwater Operation:

The ionic polymer-metal composite (IPMC) for flexible hydrodynamic propulsor blades can provide many new opportunities in navy platforms, especially in unmanned, robotic vehicles used in surveillance and combat. When in operation, the IPMC materials are very quiet since they have no vibration causing components, i.e., gears, motors, shafts, etc. For small autonomous underwater vehicles (AUV), this feature is truly attractive. IPMCs are friendly to solid-state electronics and have digital programming capabilities; thus, active control is possible. Another advantage of these materials is that they can be operational in a self-oscillatory manner. However, there are several issues that still need to be addressed: propulsor design, testing, robotic control, and the theoretical modeling of the appropriate design. Currently, the IPMC is being investigated for propulsor blade applications and a propulsor model with a robust control scheme. An analytical model of a segmented IPMC propulsor was formulated to be a building block for accommodating the relaxation behavior of IPMCs and for describing the dynamics of the flexible IPMC bending actuator.

Design and Control of a Real-Time Variable Modulus Vibration Isolator

A magnetorheological elastomer (MRE-based semi-active (SA) vibration isolator is developed and tested in real-time with a SA controller, illustrating the feasibility of MRE-based isolators. While several researchers have applied MREs to tunable vibration absorbers (TVAs), little work has been done using MREs in primary isolation systems. Further, in cases where TVAs were developed, few SA controllers were implemented in proof of concept experiments. This article presents a magnetically biased MRE-based vibration isolator, which enables the device to have a fail-safe operation in the event of a power failure. To test the effectiveness of the MRE isolator, a SA controller is developed to minimize the payload velocity. A comparison by simulation of variable modulus and damping systems is also presented. Finally, experimental results are given, showing that the MRE isolator and SA controller system reduce resonances and payload velocities by 16-30% when compared to passive systems.

Nonlinear adaptive backstepping design for spacecraft attitude control using solar radiation pressure

Spacecraft and interplanetary probes orbiting at high altitudes experience forces due to solar radiation pressure, which can be used for maneuvering. This paper treats the question of large angle pitch attitude maneuvers of satellites using solar radiation torque. For pitch axis maneuver, two highly reflective control surfaces are used to generate radiation moment. Based on a backstepping design technique, a nonlinear adaptive control law is derived for the control of the pitch angle. In the closed-loop system, the pitch angle asymptotically tracks prescribed reference trajectories. Simulation results are presented to show that the adaptive control system accomplishes attitude control of the satellite in spite of the parameter uncertainties in the system.

A cylindrical ionic polymer-metal composite-based robotic catheter platform: modeling, design and control

Ionic polymer metal composites (IPMCs) are soft electroactive polymers that have recently gained considerable attention in biomedical engineering as actuators and sensors. This study focuses on modeling, design and control of a cylindrical IPMC actuator with sectored electrodes. The cylindrical IPMC allows for multi-degree of freedom motion and accurate control of the tip location that can be utilized in biomedical active catheter devices. A three-dimensional finite element model is constructed to describe the physics of cylindrical IPMC actuation. The model is implemented to conduct optimization studies that provide conceptual designs that can maximize deflection, force output, and twisting actuation. Also, a cylindrical tube-shaped IPMC is designed and fabricated. This type of IPMC offers the ability to embed a specific tool and accurately control the tool tip location, which is critical in catheter procedures. To effectively utilize the tube-type IPMC, a closed-loop control system is created based on the electromechanical model and tested in different actuation settings. To improve functionality and the user interface the control system is designed to work on a laptop touchpad.

Active Polymers: An Overview

It can be seen from the above reported research and the scale of the academic interest in active polymer materials, that they have the potential to become an indispensable part of future technological developments. With each polymer having its own niche applications, they are bound to be the materials of future. With growing emphasis on interdisciplinary research, different active materials can be combined to develop tailor-made, multifunctional properties, where single materials can act as sensors, actuators, structural elements, etc.